This project has three broad objectives: to identify biochemical and genetic mechanisms which regulate pathways of intracellular metabolism of amino acids and their organic acid derivatives in mammalian cells; to define the structural and functional features of selected apoenzymes concerned with amino acid metabolism, and, where pertinent, of their required coenzymes; and to translate these observations into information relevant to the pathophysiology, diagnosis, and treatment of specific inherited disorders. Toward these objectives, we will examine four specific problems which focus on biosynthetic and degradative events in the lysosome, the cytosol, and the mitochondrion and which depend on preparation of purified subcellular organelles and specific enzymes and coenzymes found therein. These four problems will be examined: the intracellular transport and metabolism of cobalamin (vitamin B12) and its association with cobalamin coenzyme-dependent proteins; the structure of propionyl CoA carboxylase and the relationship between disordered propionate metabolism and ammonia intoxication; the characteristics of ornithine transcarbamylase in normal and mutant hepatic cells and the details of this enzyme's biosynthesis and distribution; and the structures of cystathionine beta-synthase and the mechanisms of its interaction with pyridoxal 5' -phosphate. In some phases of this work we will pose of test hypotheses in animals or animal tissues. In others we will take our clues form sick animals, hoping to follow such inquiry both to new standing of normal biochemistry, physiology, and cell biology.